Exposure parameter obtaining method, exposure parameter evaluating method, semiconductor device manufacturing method, charged beam exposure apparatus, and method of the same

ABSTRACT

An exposure parameter obtaining method comprising forming a charged reference pattern and a plurality of charged exposure patterns at a surface region of a to-be-exposed insulation substrate by projecting a charged beam with a first incident energy using a reference pattern whose exposure parameter has been known beforehand and all of selected exposure patterns to be corrected, forming electron signal images for the charged reference pattern and the plurality of charged exposure patterns on the basis of charged particles including secondary electrons by scanning the surface of the insulation substrate with a charged beam with a second incident energy lower than the first incident energy, and creating, on the basis of the electron signal images, the exposure parameters including at least one of position, focal point, astigmatism, rotation, and magnification for all of the selected exposure patterns to be corrected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2001-117162, filed Apr. 16,2001, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an exposure parameter obtaining method incharged beam exposure using electron beams or the like, an exposureparameter evaluating method, a semiconductor device manufacturingmethod, a charged beam exposure apparatus and to a method of the same.

2. Description of the Related Art

With the recent higher-density packaging of large-scale semiconductorintegrated circuits, charged beam exposure apparatuses using a chargedparticle beam, such as an electron beam, have been put to practical use.For instance, an electron beam exposure apparatus uses a variably shapedbeam (VSB) obtained by variably shaping the cross section of an electronbeam generated at an electron beam source. The variably shaped beam isdirected onto a waver surface and deflected for scanning on the surfaceof the wafer according to a pattern data, thereby drawing a desiredpattern. That is, this type of electron beam exposure apparatus has apattern generation function of forming a pattern, hardware, on the waverfrom the pattern data, software.

Since the electron beam exposure apparatus draws a pattern by connectingexposure shots on the wafer with a variably shaped beam whose crosssection has been shaped into, for example, a rectangle or a triangle,the smaller the pattern size to be drawn, the electron beam generallyhas to be the finer. As a result, the number of exposure shots per unitarea increases and therefore the throughput tends to decrease.

On the other hand, in the case of manufacturing a semiconductor device,such as memory, which needs ultrafine pattern exposure, althoughpatterns to be exposed are fine, most of them are often composed ofrepetitions of basic patterns. Therefore, if a basic pattern or acharacter pattern, a unit of repetitive pattern, is generated by asingle shot, such an ultra-fine pattern could be exposed with arelatively high throughput, even when the basic pattern is rathercomplex.

Therefore, instead of an exposure method using a variably shaped beam,an electron beam exposure apparatus is being put to practical use whichis performed by employing a drawing method using basic patternprojection techniques. In this method, such basic pattern is called acharacter. In the exposure apparatus, an electron beam is projected ontothe wafer through a selected aperture having a character shape of a beamshaping mask. The mask has a plurality of basic patterns, or a pluralityof characters, and is called as a character projection pattern(hereinafter, referred to as a CP pattern) mask, thereby producing anelectron beam having a basic pattern section of a desired shape with asingle shot.

As described above, an electron beam exposure apparatus is being put topractical use which has employed a drawing method using characterprojection techniques for connecting basic pattern shots by exposing thepatterns repeatedly, and thereby achieving a practically highthroughput.

The total wafer drawing time of the electron beam exposure apparatus isexpressed roughly by the product of an exposure time required to exposea single character and the number of shots. Therefore, when the resistsensitivity is raised and the beam current density is increased toshorten the shooting time and the beam size is made larger to decreasethe number of shots, the drawing time is shortened. Since the characterprojection technique (hereinafter, referred to as the CP technique) fortransferring basic patterns repeatedly decreases the number of shots, ithas a higher throughput than that of the variably shaped beam technique(referred to as the VSB technique). When several hundreds CP patternsare formed on a single mask, the frequency of mask replacementdecreases, which improves the throughput remarkably. The exposure methodusing the conventional CP technique, however, has the following problem.

In the electron beam exposure apparatus using the CP technique, beforeexposure a wafer by an electron beam, the electron beam passed througheach CP pattern aperture selected from a single CP pattern mask has tobe so adjusted that the beam reaches a specific position with respect toa reference pattern previously defined on the wafer. If there is any oneof a shift in position, rotation, blurring, and a fluctuation in themagnification in the CP pattern drawn on the wafer by the electron beam,accurate pattern exposure is impossible for the CP pattern. Accordingly,it is very important to correct or offset the position on the wafer ofthe electron beam passed through each aperture corresponding to each CPpattern.

In a conventional method of correcting the position of the CP pattern,for example, an area including a microscopic mark made of a heavy metalput on a wafer is scanned with an electron beam generated at an exposureapparatus. Then, secondary electrons generated at the microscopic markat that time are detected to obtain an electron signal image of theelectron beam shape or CP pattern. Then, pattern matching between theobtained image and a reference pattern is effected. From the differencein position between them, the amount of correction of the beam exposureposition, or exposure parameter, is determined.

In a conventional method, it is necessary to generate an electron signalimage of each CP pattern by scanning the electron beam repeatedly overeach pattern selected from the mask and used for exposure. As a result,it takes a lot of time to adjust the position of each CP pattern andaccordingly it is virtually difficult to obtain the exposure parameterfor each of several hundreds CP patterns.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided anexposure parameter obtaining method comprising: selecting a plurality ofexposure patterns to be used for exposing from an exposure mask with areference pattern whose exposure parameter has been known beforehand;forming a charged reference pattern and a plurality of charged exposurepatterns at a surface region of a to-be-exposed insulation substrate byprojecting a charged beam with a first incident energy using thereference pattern and all of the selected exposure patterns to becorrected; forming electron signal images for the charged referencepattern and the plurality of charged exposure patterns on the basis ofcharged particles including secondary electrons by scanning the surfaceof the insulation substrate with a charged beam with a second incidentenergy lower than the first incident energy; and creating, on the basisof the electron signal images, the exposure parameters including atleast one of position, focal point, astigmatism, rotation, andmagnification for all of the selected CP patterns to be corrected.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 schematically shows an electron beam exposure apparatus used inan electron beam exposure method according to a first embodiment of thepresent invention;

FIG. 2 is a block diagram showing the configuration of a signalprocessing circuit section for generating exposure parameters from thesecondary electron detection signal detected at the detector of FIG. 1;

FIG. 3 is a flowchart to help explain an exposure parameter obtainingmethod in the first embodiment;

FIG. 4 shows an example of the apertures of a plurality of CP patternsselected on an exposure mask in the first embodiment;

FIGS. 5A to 5C are diagrams to help explain a method of correcting theposition of a CP pattern in the first embodiment;

FIGS. 6A to 6C are sectional views showing changes in the state of theinside of the substrate when a voltage contrast image is obtained as aresult of a specimen (an exposed substrate) being subjected to beamexposure in the first embodiment;

FIG. 7 schematically shows an electron beam exposure apparatus used in amodification of the first embodiment;

FIGS. 8A to 8C are diagrams to help explain a method of correcting theexposure position of a CP pattern related to the modification of FIG. 5;

FIGS. 9A to 9F are sectional views showing various specimens (or exposedsubstrates) usable in the modification of FIG. 8;

FIGS. 10A and 10B are diagrams to help explain method of correcting themagnification and rotation of a CP pattern related to anothermodification of the first embodiment;

FIGS. 11A to 11E are diagrams to help explain a method of correcting thefocal point of a CP pattern related to another embodiment of the presentinvention;

FIG. 12 is a flowchart to help explain a method of evaluating theaccuracy of connection between patterns in charged beam exposure todetect a shift in the connection between CP patterns in still anotherembodiment of the present invention;

FIGS. 13A and 13B show exposure patterns to help explain an evaluationmethod in the embodiment of FIG. 12;

FIGS. 14A to 14D show CP patterns to help explain a modification of theembodiment of FIG. 12;

FIG. 15 schematically shows a reduced projection charged beam exposureapparatus usable in an embodiment of the method related to the presentinvention; and

FIG. 16 schematically shows a one-fold projection charged beam exposureapparatus usable in another embodiment of the method related to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, referring to the accompanying drawings, embodiments of thepresent invention will be explained in detail.

(First Embodiment)

FIG. 1 schematically shows an electron beam exposure apparatus relatedto a first embodiment of the present invention. This apparatus is avariably shaped, CP electron beam exposure apparatus with anacceleration voltage of 5 kV.

An electron beam 14 emitted from an electron gun 1 is caused to convergeby a lens 2 a such as an electrostatic lens and passes through anaperture 3 a of, for example, a rectangular pattern in a first aperturemask 3. The electron beam 14 passed through the aperture 3 a in thefirst aperture mask 3 is formed into a shape whose cross section isrectangular. The resulting electron beam is further caused to convergeby a lens 2 b and directed to a deflector 4 a. Thereafter, the electronbeam is deflected and projected to, for example, a rectangular CPpattern aperture 5 a in a second aperture mask 5. As described above,the electron beam 14 with a rectangular cross-section formed with thefirst aperture mask 3 is deflected by the deflector 4 a over therectangular CP pattern in the second aperture mask 5, thereby realizingan electron beam with a rectangular cross section of a desired size.Similarly, the electron beam is so deflected that it passes through a CPpattern aperture of another shape in the second aperture mask 5, forexample, a triangular aperture, thereby producing an electron beam witha triangular cross section as a basic pattern from the second aperturemask 5. Thus, the electron beam passed through the mask 5 has a basicpattern.

The electron beam of the basic pattern passed through the secondaperture mask 5 is deflected back by a deflector (not shown) onto thebeam center axis going through an aperture 3A in the first aperture mask3. Then, the section of the electron beam thus centered is reduced andcaused to converge by a reduced projection lens objective 2 c. Theelectron beam from the lens 2 c is further deflected by a deflector 4 band projected at the specified position of a chip 8 on a wafer 6 on astage 7 of the electron beam exposure apparatus. At the specified chip 8on the wafer 6, a mark 12 of a heavy metal, for example, is formed.

A mirror 9 is provided on one side face of the stage 7 perpendicular to,for example, the x direction. The mirror 9 is so configured that a laserbeam from a laser interferometer 10 is split by a beam splitter 13 andprojected onto the mirror 9. The other laser beam split by the beamsplitter 13 passes through reflectors 17 a, 17 b and are projected ontoa mirror provided on another side face of the stage 7 in the y directionperpendicular to the mirror 9. With this configuration, the laser beamsreflected by the two mirrors are caused to enter the laserinterferometer 10, which enables the positions in the x and y directionsof the stage 7 to be measured at all times.

Above the stage 7, there is provided an electron detector 11. Theelectron detector 11 detects secondary electrons generated when the mark12 and the surface of an insulation film formed on the chip 8 arescanned with the electron beam 14. The detection output signal of theelectron detector 11 is sent to a signal processing unit 120 of FIG. 2,which produces an electron signal image of an exposure pattern formed onthe wafer 6 or the chip 8. This will be explained in detail later.

The apparatus is further provided with an off-axis microscope 15. AHe—Ne laser directed from a laser source (not shown) is supplied to theoff-axis microscope 15. By using the He—Ne laser, the focal point of themark 12 on the wafer 6 is measured exactly, thereby detecting theposition of the mark 12 on the wafer 6 in X, Y and Z directions.

The apparatus is further provided with a power supply 16 for applying aspecific voltage to the wafer 6 via the stage 7. When the power supply16 applies, for example, a voltage of 4 kV to the wafer 6, this makes itpossible to set the energy (or incident energy) of the electron beam 14incident on the wafer 6 to a low energy of about 1 kV.

In FIG. 2, a secondary electron detection signal generated at theelectron detector 11 is supplied to an interface (I/F) 121 in a signalprocessing circuit 120, which subjects the signal to processes,including A/D conversion and noise removal and converts the signal intodigital data. Under the control of a memory control circuit 122, thedigital data is stored in an image memory 123 in the form of secondaryelectron image data. The memory control circuit 122 is connected to asignal processing control circuit 124, which controls the memory controlcircuit 122.

On the other hand, to perform pattern matching with the secondary imagedata stored in the image memory 123, template image data has been storedin a template image memory 125 beforehand. A memory control circuit 126controlled by the signal processing control circuit 124 controls thetemplate image memory 125 in which, for example, an N number of templateimage data items corresponding to a plurality of CP patterns formed atthe second aperture mask 5 have been stored beforehand. In this case,the N template image data items include a data item corresponding to aCP pattern defined as a reference pattern and those data itemscorresponding to CP patterns being used to form exposed CP patterns onthe chip 8.

For example, the memory control circuit 126 is connected to a controlcomputer 129 in the electron beam exposure apparatus of FIG. 1 via aninterface (I/F) 127 and a bus 128. The control computer 129 generates aplurality of template image data items on the basis of the CP patterndesign data used when generating each CP pattern at the second aperturemask 5 and stores them in the template image memory 125 via theinterface (I/F) 127 and memory control circuit 126. Alternatively,normalized CP patterns of a heavy metal may be formed on a wafer byexperiments and scanned with an electron beam, thereby obtainingtemplate image data from the resulting secondary electron signal.Furthermore, since the secondary electron detection signal obtained fromthe electron detector 11 may have a blurred outline of the pattern, thetemplate image data may be stored in the form of blurred image data inorder to perform pattern matching with the blurred-outline detectionsignal efficiently. For instance, the CP pattern design data may beconverted into blurred image data by Gaussian convolution, which may bestored in the template image memory 125.

The detected secondary electron image data stored in the image memory123 and the template image data stored in the template image memory 125are supplied to a pattern matching circuit 130, which performs patternmatching under the control of the signal processing control circuit 124.In the pattern matching, for example, the template image data is movedsequentially with respect to the detected image data to find out amatching position. The position data at which the matching is completedis read out at the signal processing control circuit 124. In otherwords, the position data thus obtained denotes a mutual positionaldeviation between the detected image and the corresponding templateimage.

The position data denoting positional differences between each of thedetected image data and the corresponding template image data obtainedin this way is stored in the data storage memory 131.

On the other hand, reference data denoting reference positionaldifferences between a reference pattern and design data of the templatepatterns are formed and stored beforehand in the control computer 129.The position data stored in the data storage memory 131 and thereference data stored in the control computer 129 are used to determinepositional deviations of the exposed CP patterns as will be describedlater.

Data items representing the determined positional deviations is storedin the control computer 129 and is used as exposure parameter data. Thestored parameter data is read when the exposure apparatus operates toexpose the CP patterns on the chip 8.

Hereinafter, referring to FIGS. 2, 3, and 4, FIGS. 5A to 5C, and FIGS.6A to 6C, a method of obtaining exposure parameters in the firstembodiment using the electron beam exposure apparatus of FIG. 1 will bedescribed. In this method, a specific CP pattern or a reference patternwhose absolute position has been corrected beforehand is used. Forexample, the exposure pattern corresponding to CP pattern A of FIG. 4 isused as the reference pattern. As for other CP patterns B and C, arelative difference in position between each exposure pattern stored inthe secondary electron image memory 123 and the reference pattern isdetermined in the form of an exposure parameter. After the shift inposition is corrected using the obtained exposure parameter, exposure ismade.

First, the wafer 6 is placed on the stage 7. Then, in step S1 in theflowchart of FIG. 3, CP pattern apertures used for wafer exposure, thatis, N number of apertures for the CP patterns to be corrected, areselected on the control computer 129 from the CP pattern aperturesformed in the selected second aperture mask 5. Here, it is assumed thata triangular CP pattern B and a triangular CP pattern C obtained byrotating the CP pattern B through an angle of 180 degrees are selectedwith a rectangular CP pattern A of FIG. 4 as a reference.

Therefore, CP pattern A is defined as a pattern already subjected toabsolute position correction (or a reference pattern). The pattern datais read as template image data in the control computer 129. In thiscase, with the reference pattern A as a reference, CP pattern B and CPpattern C have been selected in step S1 as CP patterns to be corrected.Therefore, in step S2, the template image data item corresponding to CPpattern B and the template image data item corresponding to CP pattern Care read together with that corresponding to the CP pattern A in thecontrol computer 129.

The template image data read in this way is transferred via the I/F 127of the signal processing circuit 120 to the memory control circuit 126and is stored in the template image memory 125 in step S3.

Next, in step S4, the deflector 4 a is so operated that the electronbeam passes through CP pattern apertures A, B and C in the secondaperture mask 5. This causes the electron beam 14 with an incidentenergy (or first incident energy) of 5 keV to be projected at apredetermined position on a resist layer 53 applied on an insulatingfilm 52, such as a silicon oxide film, formed on the wafer 6 of FIG. 6Aso as to take the form of CP patterns A, B and C. With this projection,exposure patterns for CP patterns A, B and C are formed at the resistlayer 53 as charged patterns or charge accumulated patterns (describedlater).

FIG. 6B is a sectional view of the exposed substrate wafer 6, a specimenin step S4. In FIG. 6B, numerals 31, 32, and 33 indicate, for example,regions exposed with the exposure patterns A, B and C at the resistlayer 53.

FIG. 5A shows an ideal positional relationship between a referenceexposure pattern 31 and exposure patterns 32 and 33 when the position ofCP pattern B and that of CP pattern C have been corrected ideally withrespect to the reference exposure pattern 31. In FIG. 5A, arrows 41 and42 are relative vectors showing the positional relationship betweenexposure pattern 31 and exposure pattern 32 and between exposure pattern31 and exposure pattern 33. In FIGS. 5A to 5C, the figures inside theexposure patterns 31, 32 and 33 corresponding to CP patterns A to C areomitted for the sake of simplification.

Next, using the power supply 16, a voltage of 4 kV is applied to thewafer 6 in step S5. This decreases the necessary energy of the electronbeam 14 incident on the wafer 6 relatively to 1 keV. In this state, aregion (or CP exposure region) including the exposure patterns 31 to 33obtained in step S4 is scanned with the electron beam 14 with anincident energy (or second incident energy) of 1 keV. Of secondaryelectrons and reflected electrons from the electron detector 11,secondary electrons mainly represent the exposed patterns. The detectionsignal is sent to the signal processing unit 120, which processes thesignal and produces a potential contrast image as a secondary electronsignal image. The secondary electron image data obtained in this way isstored in the secondary electron image memory 123.

Referring to FIG. 6C, explanation will be given as to how secondaryimage data about CP patterns A to C are obtained by twice electron beamexposures in step S4 and step S5.

In step S4, an electron beam with a high energy is projected onto theinsulation photosensitive resist 53 formed on the insulating film 52 onthe semiconductor substrate 6 of FIG. 6A. Then, as shown in FIG. 6B,charged portions of the part where exposure patterns 33 are formedthrough the projection of the electron beam. For example, in the case ofsuch a resist as a chemically amplified resist where sensitized materialgenerates ions as a result of exposure, the conductivity of the exposedpart increases. Therefore, the charges are accumulated at the exposedportions.

Then, the whole part is scanned with an electron beam with a low energyin step S5.

FIG. 6C is a sectional view of the specimen in step S5. In FIG. 6C,numeral 54 indicates a region (or scanning region) lightly re-exposed bythe scanning of the electron beam 14 with the second incident energy (orlow incident energy). Since the resist 53 is an insulating material or adielectric material, scanning with such a low energy beam normallycauses the charge of the electron beam to be accumulated at the surfaceof the resist 53. As a result, a shallow charged layer 54 is formed atthe surface of the resist 53 as shown in FIG. 6C.

Since the part of the patterns 31 to 33 exposed with the first highenergy as described above has a higher conductivity, the chargeaccumulated on the part leaks toward the substrate 6 into the patterns31 to 33. As a result, the charges at the surface of the resist 53corresponding to the patterns 31 to 33 are accumulated, resulting in agreat contrast with the unexposed part in terms of the amount of chargeat the surface. The emission efficiency of secondary electrons dependson the surface potential of the resist 53.

Therefore, when the whole part is scanned with the low energy electronbeam for the second time, the amount of secondary electrons detected bythe electron detector 11 corresponds to the exposure pattern formed atthe resist 53. As a result, the electron detector 11 detects exposurepatterns in the form of the strength and weakness of a secondaryelectron signal.

While in the embodiment, a resist where the conductivity of the exposedpart varies according to exposure has been used, such an insulating filmas an Si dioxide film may be used instead of the photosensitive resist53. In the case of the Si dioxide film, many charges are accumulated inthe part on which the electron beam has been projected. Consequently,the exposed part has a negative potential with respect to the unexposedpart, resulting in a contrast in the surface potential. In this case,too, the exposure patterns are detected in the form of the strength andweakness of the secondary electron signal.

Specifically, in FIG. 6C, inside the re-exposed region 54 shallowlyformed at the surface of the resist layer 53, the permittivity of thepart in which exposure patterns 31 to 33 have been formed differs fromthat of the unexposed part. Therefore, when scanning is done with theelectron beam 14 with an incident energy of 1 keV, the electric fieldappearing between the wafer 6 and the surface of the layer varies withthe permittivity and therefore the amount of electrification varies fromregion to region. The difference in the amount of electrification causesa voltage contrast. As a result, the amount of secondary electronsgenerated as a result of the scanning of the electron beam 14 varieswith the voltage contrast, thereby forming electron signal image data atthe signal processing unit 120 according to the amount of electronsdetected according to the exposure patterns 31 to 33.

The electron signal image obtained at the signal processing circuit 120according to the difference in the amount of electrification between theexposure patterns 31 to 33 on which the electron beam 14 has beenprojected and the unexposed region at the resist layer 53, that is, thedifference in surface potential between the exposed regions 31 to 33 andthe unexposed region, is defined as a voltage contrast image.

The secondary electron image data about the patterns A to C obtained inthis way is stored in the secondary electron image memory 123 in stepS6.

Since each side of the square including the exposure patterns 31, 32,and 33 was 5 μm in length, the scanning area of the electron beam 14 wasset to 20 μm□. To obtain an electron signal image, a special CP mask wasselected and beam scanning was so effected that the electron beam 14with the second incident energy took the form of a round beam of about0.05 μmφ on the wafer 6.

As shown in FIG. 5B, it is assumed that, as shown by arrows 41′ and 42′,the positions of exposure patterns B and C have deviated from the normalpositions shown by broken lines to the positions shown by solid lineswith respect to the exposure pattern 31 corresponding to CP pattern A, areference pattern. Specifically, relative vectors 41′ and 42′representing the positional relationship between pattern 31 and actualexposure patterns 32′, 33′ obtained by exposure using exposure patternsB and C are determined as data representing a shift in position. Sincethe exposure pattern 31 is obtained with CP pattern A subjected toabsolute position correction, it has no shift in position. Exposurepatterns 32′ and 33′ have a shift in position.

For example, the secondary electron image data including the CP patternsA, B and C is read from the memory 123. At the same time, in step S7,the normal template image data 32 corresponding to CP pattern B is readfrom the template image memory 125. Then, Both of these data are sent tothe pattern matching circuit 130.

In the pattern matching with respect to the exposed pattern 32′, forexample, the template image data corresponding to the pattern 32 ismoved sequentially with respect to the detected image data of thepattern 32′ to find out a matching position. The position data at whichthe matching is completed is read out at the signal processing controlcircuit 124. The position data about the template image pattern whichhas matched with the pattern 32 is the position of exposure pattern 32′to be determined. As a result, in step S9, the position data aboutexposure pattern 32′ is obtained. The position data passes through thesignal processing control circuit 124 and is stored in the data storagememory 131.

Similarly, as for all the exposure patterns including the remainingselected exposure patterns 31 and 33, the processes in step S7 and stepS9 are carried out. When the fact that the position data about theexposure patterns for all of the N number of CP patterns selected instep S10 has been stored in the data storage memory 131 is detected, theprocess proceeds to step S11.

In this state, for example, the ideal or designed position data aboutexposure patterns A, B and C as shown in FIG. 5A is read. On the otherhand, the position data about reference pattern 32′ is read from thedata storage memory 131 and sent via the I/F 132 to the control computer129. The control computer 129, in step S12, calculates data about theamount of a shift in position corresponding to the vector 43 shown inFIG. 5B.

Then, the control computer 129 calculates an offset or a correctionvalue for correct the difference in position between pattern 32 andpattern 32′ on the basis of the data about the amount of a shift inposition obtained in step S12. The data about the correction valuecalculated for exposure pattern B is stored in the memory of the controlcomputer 129 or in the data storage memory 131.

Similarly, data about the correction value for exposure pattern C iscalculated in step S11 to S13 from the position of reference exposurepattern 33 and that of exposure pattern 33′ shown in FIG. 5B. The resultis stored in a specified memory.

When the fact that, of the selected N exposure patterns, the data aboutthe correction values for (N−1) exposure patterns excluding thereference pattern have been stored in the memory is detected in stepS14, the process of obtaining the exposure parameter data is completed.

Thereafter, the application of a voltage from the power supply 16 isstopped. With a desired acceleration voltage, the exposure pattern 5 aof the second aperture mask 5 is exposed in FIG. 1. At this time, thecorresponding correction value data is read from a specific memory instep S15. As a result, the position of the CP exposure pattern on thewafer 6 is corrected with the electron beam 14 by, for example, drivingthe deflectors 4 a, 4 b, which enables the exposure patterns 32, 33 tobe exposed in the proper positions with respect to the reference pattern31 in step S16 as shown in, for example, FIG. 5C.

Hereinafter, operational advantages obtained when exposure in the firstembodiment is made will be described.

(1) Firstly, it is not necessary to measure the shape of the beam usinga microscopic mark differently from the prior art. In the prior art, ittakes several minutes to measure the shape of the beam for each CPpattern. Thus, it is difficult to adjust several hundred CP patterns ina short time. In the first embodiment, however, the relative positionbetween CP patterns can be measured only by an ordinary exposureprocess, which enables very high speed processing. As a result, theproductivity in electron beam exposure can be improved.

(2) Secondly, the first embodiment may be applied to a case where thesurface of a specimen to be exposed is made of a dielectric material, ora chargeable material. For pattern transfer, a resist, a dielectricmaterial, is normally applied to a wafer to be exposed. This means thatthe position between CP patterns can be corrected using the wafer to beexposed. In the conventional method using a microscopic mark,corrections were needed as a result of adjusting the height of themicroscopic mark and that of the wafer to be exposed. In contrast, withthe first embodiment, since adjustment can be made at the wafer to beexposed, the drawing accuracy can be improved.

(3) Thirdly, all beam adjustments in the first embodiment can be madeconsecutively in the exposure apparatus. Moreover, the processing can bedone at very high speeds. Consequently, the beam can be corrected easilyduring drawing. This makes it possible to shorten remarkably the timefrom when the beam is corrected until exposure is started and reducesufficiently the change of the exposure apparatus with time after beamcorrection. Accordingly, it is possible to increase the drawing accuracyremarkably as compared with the prior art.

With such a configuration, since only one scanning is needed todetermine exposure parameters used to adjust a plurality of CP patternsin an exposure mask, it is possible to adjust the selected exposurepatterns in a short time.

The reason why only one scanning is needed is that scanning with acharged beam whose incident energy is lower than that of the chargedbeam projected in forming an exposure pattern prevents the exposurepattern from disappearing and that the amount of electrification in thesensitized area of an exposure pattern (composed of an area sensitizedby a charged beam and an unsensitized area) differs from that in theunsensitized area, which produces an electron signal image correspondingto the exposure pattern.

Next, another embodiment of the exposure apparatus and method will beexplained. While in the above embodiment, the electron beam exposureapparatus of FIG. 1 has been used, an electron beam exposure apparatusshown in FIG. 7 may be used. This apparatus uses an observation SEM(scanning electron microscope) 20 as a pattern observation electron beamscanning section instead of using the power supply 16 shown in FIG. 1which applies a voltage to the wafer 6. The observation SEM 20, whichincludes an electron gun 21, a lighting and objective system 22 a, 22 b,and a deflector 23, can scan a desired area on the wafer 6 with theelectron beam 24 with an acceleration voltage of 1 kV. Although theobservation SEM 20 is used as the electron beam scanning section, thepresent invention is not limited to this. For example, the observationSCM 20 may be useful in conjunction with the power supply 16.

While in the above exposure method, the exposure pattern for the CPpattern subjected to absolute position correction is used as a referencepattern and a relative shift in position of the exposure pattern for theCP pattern to be corrected from the reference pattern is determined,another method may be used. For instance, a mark (or reference mark)formed on a dielectric material may be used as a reference pattern andthe amount of the shift of a CP pattern to be corrected from thereference mark may be determined. Hereinafter, this modification will beexplained concretely using a case where the electron beam exposureapparatus of FIG. 1 is used.

FIGS. 8A to 8C show drawings corresponding to FIGS. 5A to 5C. In FIGS.8A to 8C, the parts corresponding to those in FIGS. 5A to 5C areindicated by the same reference numerals and a detailed explanation ofthem will not be given. Similarly, in the drawings after FIGS. 8A to 8C,the same reference numerals as in the preceding drawings indicate thecorresponding parts and a detailed explanation of them will not begiven.

FIG. 8A shows a reference mark 61, an exposure pattern 32, and anexposure pattern 33. The reference pattern 61 is a pattern serving as areference in correcting absolute positions. The exposure patterns 32, 33show the exposure patterns for CP patterns B and C to be corrected.

FIG. 8A shows an ideal positional relationship between reference mark 61and exposure patterns 32, 33 when the position of CP pattern B and thatof CP pattern C have been corrected ideally. In FIG. 8A, arrows 71 and72 are relative vectors showing the positional relationship betweenreference mark 61 and exposure pattern 32 and between reference mark 61and exposure pattern 33.

FIGS. 9A to 9F show concrete examples of a reference mark. In FIG. 9A, agroove 61 a in the surface of an insulating film 52, such as a siliconoxide film, is used as a reference mark. In FIG. 9B, a projectingpattern 61 b at the surface of the insulating film 52 is used as areference mark. In FIG. 9C, a conductive member 61 c buried in a groovein the surface of the insulating film 52 and made of a differentmaterial from that of the insulating film 52 is used as a referencemark. In FIG. 9D, a conductive member 61 d provided in a deep positionfrom the flat surface of the insulating film 52 and made of a differentmaterial from that of the insulating film 52 is used as a referencemark. In FIGS. 9E and 9F, a groove 61 e and a groove 61 f in the surfaceof an Si substrate 51 are used as a reference mark, respectively. FIG.9E shows a case where the insulating film 52 buried in the groove 61 eis thick and has a flat surface. FIG. 9F shows a case where theinsulating film 52 buried in the groove 62 f is thin and has a recessedpart at its surface corresponding to the groove 61 f. Numeral 56 in thefigure indicates a charged area formed by exposure at the surface of thespecimen.

In this modification, a CP beam positioning method (or a beam correctionmethod) is carried out as follows. The method is basically the same asin the above embodiment.

First, a plurality of CP patterns to be corrected are selected. Forexample, CP patterns B and C are selected as CP patterns to becorrected.

Then, the electron beam 14 with an incident energy (or a first incidentenergy) of 5 keV is projected onto a wafer (or specimen) 6 via CPpattern B and CP pattern C on the basis of design data, thereby formingexposure patterns 32, 33.

Next, using the power supply 16, a voltage of 4 kV is applied to thewafer 6. As a result, the energy of the electron beam 14 incident on thewafer 6 decreases to 1 kev. In this state, the SCM image including thereference mark 61, exposure pattern 32, and exposure pattern 33 isobtained. A detector 11 and a signal processing unit (not shown) obtainan electron signal image (or a potential contrast image).

Next, as shown in FIG. 8B, the positional relationship (=relative vector71′) between the reference mark 61 and exposure pattern 32′ isdetermined on the basis of the obtained electron signal image.

To determine the degree of a shift in position, the difference betweenthe exposure pattern 32 and the exposure pattern 32′ (=relative vector71′−relative vector 71 =vector 73) is found. As a result, the amount(Δx, Δy) of correction of the position of CP pattern B necessary tocause exposure pattern 32′ to coincide with exposure pattern 32 isobtained. In measuring the position of the pattern at that time, knownpattern matching using each CP pattern figure as a template file wasused. Similarly, the amount of correction of the position is determinedfor the remaining selected exposure pattern 33.

Next, the application of a voltage from the power supply 16 is stopped.With a desired acceleration voltage, the position of each CP pattern iscorrected on the wafer 6 (or on the surface of the specimen) on thebasis of the amount of correction of each position, thereby formingexposure patterns 32 and 33 in desired positions as shown in FIG. 8C.This modification also produces the same effect as in the embodiment.

While in the embodiment, the position of a CP pattern, one of theexposure parameters, has been corrected, the present invention may beapplied to the correction of another exposure parameter.

For example, as shown in FIG. 10A, the magnification of a CP pattern maybe corrected using known pattern matching on the basis of the obtainedelectron signal image. Moreover, as shown in FIG. 10B, the rotation of aCP pattern may be corrected using known pattern matching on the basis ofthe obtained electron signal image. In FIGS. 10A and 10B, exposurepatterns 82, 84, and 86 show ideal exposure patterns. In FIG. 10A,exposure patterns 81, 83, and 85 represent enlarged and reduced patternsactually obtained through exposure. FIG. 10B shows rotating patternsobtained through exposure.

(Second Embodiment)

In the first embodiment, the method of correcting the position of a CPpattern has been explained. The present invention may be applied to amethod of correcting the focal point of a CP pattern as one of apositional data. Hereinafter, using FIGS. 11A to 11E, a method ofadjusting the focal point according to the present invention will beexplained. A case where the electron beam exposure apparatus of FIG. 1is used will be explained.

First, a CP pattern whose focal point is to be adjusted is selected. Asshown in FIG. 11A, a line-and-space pattern is selected as a CP pattern91 to be subjected to focus adjustment.

Next, with an incident energy of 5 keV, an exposure pattern for a CPpattern 91 is formed on a specimen wafer 6 on which an insulating film52 has been formed as in the fist embodiment. At this time, as shown inFIG. 11B, the position of the focal point and the position of exposureon the surface of the specimen 6 are changed so as to form five exposurepatterns 91 a to 91 e. A silicon oxide film is used as the insulatingfilm 52.

Then, with the power supply 16, a voltage of 4 kV is applied to thewafer 6. As a result, the energy of the electron beam 14 incident on thewafer 6 decreases to 1 keV. In this state, an area including exposurepatterns 91 a to 91 e are scanned one-dimensionally (or linearly),thereby detecting the electron signal images of the exposure patterns 91a to 91 e at a time.

FIG. 11C shows an intensity distribution of an exposure beam for each ofthe CP patterns 91 a to 91 e. When an exposure beam is projected ontothe surface of the insulating film 52, a potential distributiondependent on the beam intensity distribution is formed at the surface ofthe insulating film 52. Scanning the surface of the insulating film 52with an electron beam with a low energy of about 1 keV enables asecondary electron signal to be obtained according to the surfacepotential distribution. As a result, a secondary electron signaldistribution can be obtained as shown in FIG. 11D.

In FIG. 11D, numeral 91 c′ indicates a secondary electron signaldistribution when the electron beam is best focused. Numeral 91 a′indicates a secondary signal distribution when the beam is most out offocus. For example, plotting the contrast of the secondary electronsignal obtained at the position of each focal point produces therelationship between the position of the focal point and the contrast asshown in FIG. 11E. In the plotting of FIG. 11E, the steepest part of thesecondary electron signal (a hill part of the secondary electron signalwhere the maximum value—minimum value of the signal strength becomes thelargest), that is, a part as shown by 91 c′ in FIG. 11D, is found,thereby determining the optimum position of the focal point.

Thereafter, the application of a voltage from the power supply 16 isstopped. With a desired acceleration voltage, the CP pattern is exposedon the basis of the optimum position of the focal point.

The second embodiment provides the same operational advantages (1) to(3) as in the first embodiment. While in the second embodiment, theoptimum position of the focal point has been determined on the basis ofthe contrast of the secondary electron signal, it may be determined inanother way. For instance, the inclination (or the beam resolution) ofthe secondary electron signal may be found, thereby determining theoptimum position of the focal point.

(Third Embodiment)

In a third embodiment of the present invention, a case where the presentinvention is applied to a method of evaluating the accuracy ofconnection (or stitching accuracy) between patterns in charged beamexposure will be explained by reference to FIGS. 12, 13A, and 13B. Avariably shaped, CP electron beam exposure apparatus with anacceleration voltage of 50 kV is used. The basic configuration of theapparatus is the same as that of the electron beam exposure apparatus ofFIG. 7.

Hereinafter, a method of evaluating the accuracy of connection betweenpatterns in the third embodiment will be explained by reference to aflowchart in FIG. 12. First, the beam for each CP pattern is corrected(step S21) and a wafer is transferred (step S22).

Next, a CP connection evaluation mask is selected as a CP pattern. Anelectron beam with a first incident energy is projected via the maskonto a chip, thereby exposing the CP connection evaluation pattern,which produces an exposure pattern (step S23).

FIG. 13A shows the positional relationship between exposure patterns 101and 102 when the CP connection evaluation pattern has been exposedideally. FIG. 13B shows the positional relationship between exposurepattern 101 a and exposure pattern 102 b which have been actuallyexposed. In FIG. 12B, Δx indicates a shift (an exposure parameterrelated to position) in the connection between exposure pattern 101 aand exposure pattern 102 b.

Next, using an observation SEM 20, electron signal images (or potentialcontrast images) of exposure pattern 101 a and exposure pattern 102 bare obtained (step S24). The incident energy (or a second incidentenergy) of the electron beam used for the observation SEM 20 is lowerthan the first incident energy.

Next, the accuracy of the connection between exposure pattern 101 a andexposure pattern 102 b is evaluated (step S25). If the result of theevaluation has exceeded a specified value, the beam is corrected (stepS26) and the accuracy of the connection is evaluated again. If theresult of the evaluation is within the specified value, the exposure iscontinued and thereafter the wafer 6 is carried out (step S27). Theremaining wafers are also subjected to steps S22 to S27.

Hereinafter, the operational advantages in making exposure in the thirdembodiment will be described.

In correcting the CP beam in the prior art, a wafer (or specimen) wasput outside an exposure apparatus. After processes, includingdevelopment, were carried out, the accuracy of the connection ofpatterns was measured. In the third embodiment, however, the accuracy ofthe connection between patterns can be evaluated without putting thewafer outside the exposure apparatus. This enables the beam accuracy tobe evaluated precisely, which improves the productivity.

Since the above approach enables exposure to be made in the optimumstate all the time, a high-accuracy drawing can be performed. Theabove-described process has only to be carried out according to apredetermined sequence in the course of exposing the wafer (orspecimen). For instance, making an evaluation before starting to exposeeach wafer enables a high-accuracy exposure to be realized.

While in the third embodiment, a special pattern has been used inevaluating the connection, the present invention is not limited to theshape of the pattern. Even when a pattern of another complex shape isused, the connection can be evaluated.

For instance, CP pattern A103 and CP pattern B104 as shown in FIGS. 14Aand 14B may be used. As shown in FIGS. 14C and 14D, exposure pattern 103and exposure pattern 104 are arranged in a nesting manner. With thisnest of patters, the surface of the dielectric material, such as theinsulating film 52, is exposed. Use of this method enables the totalexposure area of the pattern to be saved. This makes it possible tomeasure many exposure patterns simultaneously.

The present invention is not limited to the above embodiments. Forinstance, the invention is not restricted by the shape of the beam usedin the charged beam exposure apparatus. As for the electron beam withthe first incident energy, the invention may be applied to a variablyshaped beam, a round beam, a penetrating beam from a reduced or one-foldprojection mask, and a scattered beam. Furthermore, as for the electronbeam with the second incident energy, an exposure pattern may beobserved (or an electron signal image may be obtained) with an CP beamother than a round beam or a rectangular beam. A pattern (or anaperture) for forming a CP beam or a rectangular beam is formed in asecond aperture beforehand.

In addition, the present invention is not limited to the shape or sizeof a CP pattern to be evaluated.

Furthermore, the present invention is not limited to the form of thecharged beam exposure apparatus. For instance, the invention may beapplied to the use of a reduced projection charged beam exposureapparatus which has a stencil or a membrane mask stage 111 and apenetration or membrane mask 112 at which all the desired circuitpatterns have been formed as shown in FIG. 15, or to the use of aone-fold projection charged beam exposure apparatus with a one-foldtransfer mask 113 as shown in FIG. 16.

Furthermore, the present invention is not limited to the accelerationvoltage for the charged beam. The incident energy (or the first incidentenergy) of a charged beam for exposure may be 5 keV or less or 50 keV ormore. In the step of obtaining an electron signal image, the incidentenergy (or the second incident energy) may be 1 keV or less or 1 keV ormore. Here, the condition of the first incident energy>the secondincident energy must be fulfilled.

The present invention may be applied not only to drawing directly on awafer but also to exposure of a photomask. An object to be exposed isnot limited to a wafer.

The invention may be applied to, for example, an exposure method using acharged beam other than an electron beam, such as an ion beam.

In the above embodiments, two or more exposure parameters, includingposition, focal point, astigmatism, rotation, and magnification, not oneexposure parameter, may be obtained simultaneously. Thereafter,correction, evaluation, or exposure may be made.

The above embodiments include various stages of the invention. Bycombining a plurality of disclosed structural requirements suitably,various invention can be extracted. For instance, even when some areeliminated from all of the structural requirements, if the object of thepresent invention can still be achieved, the configuration less theeliminated structural requirements is extracted as an invention. Inaddition, the present invention may be practiced or embodied in stillother ways without departing from the spirit or essential characterthereof.

As has been described in detail, with the present invention, it ispossible to realize a parameter exposure obtaining method useful inadjusting the exposure mask in a short time, an exposure parameterevaluating method, and a highly productive charged beam exposure method.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. An exposure parameter obtaining method comprising: selecting aplurality of exposure patterns to be used for exposure from an exposuremask with a reference pattern whose exposure parameter has been knownbeforehand; forming a charged reference pattern and a plurality ofcharged exposure patterns at a surface region of a to-be-exposedinsulation substrate by projecting a charged beam with a first incidentenergy using the reference pattern and all of the selected exposurepatterns to be corrected; forming electron signal images for the chargedreference pattern and the plurality of charged exposure patterns on thebasis of charged particles including secondary electrons by scanning thesurface of the insulation substrate with a charged beam with a secondincident energy lower than the first incident energy; and creating, onthe basis of the electron signal images, the exposure parametersincluding at least one of position, focal point, astigmatism, rotation,and magnification for all of the selected exposure patterns to becorrected.
 2. The exposure parameter obtaining method according to claim1, wherein said creation of exposure parameters defines an exposurepattern for a specific exposure pattern as a reference pattern, anddetermines a vector representing the relative positional relationshipbetween the defined reference pattern and an exposure pattern to becorrected.
 3. The exposure parameter obtaining method according to claim2, further comprising evaluating said exposure pattern on the basis ofsaid obtained vector.
 4. The exposure parameter obtaining methodaccording to claim 2, wherein said correction of the reference patternis made by use of said specific exposure pattern so as to correct theexposure parameter for an exposure pattern obtained on the exposedsubstrate.
 5. The exposure parameter obtaining method according to claim2, wherein said correction of the specific exposure pattern is made byuse of a reference mark formed on said substrate.
 6. The exposureparameter obtaining method according to claim 1, wherein said exposureby a charged beam with said first and said second incident energy ismade on an insulating film formed on said exposed substrate.
 7. Theexposure parameter obtaining method according to claim 6, wherein saidobtaining of electron signal images is effected on the basis of thedifference in the amount of electrification between a part exposed by acharged beam with said first incident energy and an unexposed part, whensaid insulating film is scanned with a charged beam with said secondincident energy.
 8. The exposure parameter obtaining method according toclaim 6, wherein said formation of exposure patterns is made to a firstdepth at said insulating film formed on said exposed substrate with acharge beam with said first incident energy, and said obtaining ofelectron signal images exposes said insulating film uniformly to asecond depth shallower than said first depth with a charged beam withsaid second incident energy and forms a voltage contrast image accordingto the difference in the amount of electrification at the insulatingfilm to said second depth caused by the projection of the charged beamwith said second incident energy according to a phase change in theinsulating film arrived at said first depth.
 9. The exposure parameterobtaining method according to claim 8, wherein said creation of exposureparameters is performed by producing the difference between a voltagecontrast image of said reference exposure pattern and a voltage contrastimage of said exposure pattern by pattern matching.
 10. The exposureparameter obtaining method according to claim 1, wherein said selectedexposure patterns are character projection (CP) patterns.